Cells make up every living things. One important part of a cell is the cell membrane. The cell Membrane is a thin protective coating around a cell that regulates what goes in and out of the cell. An important part of regulating this is passive transport. Passive transport is the movement of materials through membranes without any input of energy. One type of passive transport is diffusion. Passive transport is the diffusion of substances across a membrane. In diffusion, molecules will usually move from where the substance is more concentrated to where it is less concentrated. The molecules also tend to spread out in the space they enter just like food coloring in water. Water diffuses freely across membranes, an obvious benefit for cells since water is crucial to many cellular processes. Some molecules however must be helped across the cell membrane through a process called facilitated diffusion. Another type of passive transport is facilitated diffusion. Facilitated diffusion is the type of passive transport that allows substances to cross cell membranes with the help of special transport proteins. The proteins help let in molecules that would otherwise not be able to get in. The last kind of diffusion is osmosis. In plant cells, water is constantly diffusing into the cell. If the concentration of water is higher outside the cell than inside, water moves into the cell. If the concentration of water is lower outside a cell, water moves out of the cell. It is easy to see the effects of osmosis on plants. When you forget to water the plant, the soil becomes dry. If the soil is dry, there is no water to soak up. As a result, the water leaves the plant through osmosis leaving it wilted. This means the leaves will shrink. If you water the plant, it will soak up all the water through osmosis and it will look normal again. Cells benefit from passive transport because some materials can move through various cell membranes without any input of energy....

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...Diffusion, Osmosis, Active Transport
There are two ways in which
substances can enter or leave a
cell:
1) Passive
a) Simple Diffusion
b) Facilitated Diffusion
c) Osmosis (water only)
2) Active
a) Molecules
b) Particles
DiffusionDiffusion is the net passive movement of particles (atoms, ions or
molecules) from a region in which they are in higher concentration to
regions of lower concentration. It continues until the concentration of
substances is uniform throughout.
Some major examples of diffusion in biology:
• Gas exchange at the alveoli — oxygen from air to blood, carbon
dioxide from blood to air.
• Gas exchange for photosynthesis — carbon dioxide from air to
leaf, oxygen from leaf to air.
• Gas exchange for respiration — oxygen from blood to tissue cells, carbon dioxide in
opposite direction.
• Transfer of transmitter substance — acetylcholine from presynaptic to postsynaptic
membrane at a synapse.
• Osmosis — diffusion of water through a semipermeable membrane.
High Diffusion Rate: short distance, large surface area, big concentration difference (Fick’s Law).
High temperatures increase diffusion; large molecules slow diffusion.
Facilitated Diffusion
This is the movement of specific molecules down a concentration gradient, passing through the
membrane via a specific carrier protein. Thus, rather like
enzymes, each...

...DIFFUSION REVIEW WORKSHEET
1. Define diffusion and what causes it to occur?
The action of spreading the light from a light source evenly so as to reduce glare and harsh shadows. Diffusion is caused when entities are small and moving in molecules. They collide because they are moving at a random pace. The temperature causes diffusion.
2. Define the terms hypertonic, hypotonic, and isotonic solution.
* Hypertonic: Having increased pressure or tone, in particular.
* Hypotonic: Having reduced pressure or tone, in particular.
* Isotonic solution: a solution having the same osmotic pressure
3. Explain the similarities and differences between diffusion and osmosis.
Both are the movement of a substance from an area of high concentration to an area of low concentration. But osmosis is the movement of water through a cell membrane.
4. Define Turgor pressure ( also known as osmotic pressure).
The pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution
5. What occurs when plasmolysis takes place?
The cells shrink and shiver.
6. Define the terms endocytosis and exocytosis .
* Endocytosis: the taking in of matter by a living cell by its membrane to form a vacuole.
* Exocytosis: Large molecules that are manufactured in the cell are released...

...LAB EXERCISE: Diffusion and Osmosis
Laboratory Objectives
After completing this lab topic, you should be able to:
1. Describe the mechanism of diffusion at the molecular level.
2. List several factors that influence the rate of diffusion.
3. Explain why diffusion is important to cells.
4. Describe a selectively permeable membrane, and explain its role in osmosis.
5. Define hypotonic, hypertonic, and isotonic in terms of relative concentrations of
osmotically active substances.
6. Discuss the influence of the cell wall on osmotic behavior in cells.
7. Explain how incubation plant tissues in a series of dilutions of sucrose can give an
approximate measurement of osmolarity of tissue cells.
8. Explain why osmosis is important to cells.
Introduction
Maintaining the steady state of a cell is achieved only through regulated movement of materials through cytoplasm, across organelle membranes, and across the plasma membrane. This regulated movement facilitates communication within the cell and between cytoplasm and the external environment.
The cytoplasm and extracellular environment of the cell are aqueous solutions. They are composed of water, which is the solvent, or dissolving agent, and numerous organic and inorganic molecules, which are the solutes, or dissolved substances. Organelle membranes and the plasma membrane are selectively permeable, allowing water to freely pass through but...

...DIFFUSION AND OSMOSIS: WHAT’S TO EXPECT?
Diffusion and osmosis are very important in biological process. Diffusion is the movement of molecules or ions from a region of their high concentration to a region of their low concentration. Osmosis is the diffusion of water molecules across a semipermeable membrane. To gain a better understanding of diffusion and osmosis, we examine multiple experiments to showdiffusion and osmosis in animal cell, plant cell and synthetic cell. In our first experiment, we weight a decalcified chicken egg and place 10% NaCl concentration. At every fifteen minutes intervals, we weight the egg and record that the weight decreases. In our second experiment, we use three slices of aquatic plant Elodea and add pond water one leaf, distilled water for the second and 20% NaCl for the third, then observe the cells of each leaf with a compound microscope. Under microscope, chloroplasts (green organelles) in Elodea tend to bound to the cell wall in pond water, spread all over the cell in distilled water, pull away from cell wall in 20% NaCl. In our last experiment, we use a dialysis bag that contains 30% glucose and starch solution then place into a beaker of water and iodine solution. We then remove the bag out of the beaker, and use two test tube which label BAG, BEAKER to perform a Benedict’s test. We place solution in the bag in the BAG tube, and solution in the...

...Lesson I learned that the primary structure of a cell membrane is made up of a double layer of phospholipids molecules. The hydrophilic heads of the phospholipid molecules face outwards towards the water base solutions inside and outside the cell. The membrane is also made up of proteins, carbohydrate molecules, and cholesterol that form gates and pores, cell recognition, and stability. Active transport is used when a cell needs a substance to cross the membrane against its concentration gradient using protein carriers. Examples of active transport are endocytosis, exocytosis, and phagocytosis. Passive transport does not require energy it is powered by the concentration gradient of the molecule. Examples of passive transport are diffusion, facilitated diffusion, filtration, and osmosis.
In our Osmosis Lab I used a Grade a large egg from the grocery store. Its circumference is 5 ½ inches it is smooth with no cracks. I carefully place the egg in a clear plastic cup and fill the cup with vinegar. I immediately notice bubbles covering the egg and sifting upwards towards the top of the cup, looking through the cup I can see the egg is slightly suspended in the liquid. Within 25 hours there was white foam covering the egg. I cannot see the egg looking directly down. Through the cup I see the egg is still covered in bubble and is still slightly suspended. The next 48 hours there is still foam on the surface with what I can make out is pieces of the...

...Lab Report on Osmosis and Diffusion
Biology 1, Period 3 March 15, 2010
Lab Team: Jason Perez, Kicia Long, Chris McLemore
Purpose:
The purpose of this lab is to observe the acts of passive transport: diffusion and osmosis in a model membrane system. The experiment will show how molecules in solution move from areas of higher concentration to areas of lower concentration. The model membrane is dialysis tubing.
Materials Used
2.5 cm dialysis tubing 15% glucose solution glucose test strip
1% starch solution distilled water Lugol’s iodine solution
Procedure:
Each member of the lab group will complete the procedures independently
1. Obtain a 30 cm piece of 2.5-cm dialysis tubing that has been soaking in water. Tie off one end of the tubing to form a bag. To open the other end of the bag, rub the end between your fingers until the edges separate.
2. Place 15 mL of the 15% glucose/1% starch solution in the bag. Tie off the other end of the bag, leaving sufficient space for the expansion of the contents in the bag. Record the color of the solution and weight of the bag in a data table.
3. Test the 15% glucose/1% starch solution for the presence of glucose using a test strip. Record the results in the data table.
4. Fill a 250 mL beaker or cup two-thirds full with distilled water. Add approximately 4 mL of Lugol's solution to the distilled water and record the color of the...

...Diffusion Experiment: Osmosis in Sucrose Solutions
Abstract
We used dialysis tubing to simulate a semi-permeable membrane. Since molecules diffuse from their higher concentration to their lower concentration, water will move across the membrane in response to this concentration. While conducting this lab we were able to observe passive transport through diffusion and osmosis.
Introduction Osmosis is a specialized case of diffusion that involves the passive transport of water. When osmosis occurs water moves through a selectively permeable membrane from a region of its higher concentration to a region of its lower concentration. The membrane selectively allows passage of certain types of molecules while restricting the movement of others. This experiment is a great way to demonstrate the process of osmosis and to show evidence of osmosis occurring over time. We simulated a semi-permeable membrane by using dialysis tubing, which allows small molecules such as water to pass through, but does not allow larger molecules such sucrose to cross. To see if osmosis will occur when there is an imbalance of concentrations on opposite sides of the membrane, we filled the dialysis tubing with various concentrations of sucrose. Our hypothesis was that with a water concentration gradient across the membrane, osmosis will occur. If water crosses into the tubing, the tubing will can weight over time. If the concentration...

...Diffusion and Osmosis
NGSSS:
SC.912.L.14.2 Relate structure to function for the components of plant and animal cells. Explain the role of cell membranes as a highly selective barrier (passive and active transport).
SC.912.L.14.3 Compare and contrast the general structures of plant and animal cells. Compare and contrast the general structures of prokaryotic and eukaryotic cells. AA
Background: (Source: www.explorelearning.com)
Diffusion is the process in which there is a net movement of molecules from a high area of concentration to a low area of concentration. Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane (Semi-permeable membranes are very thin layers of material which allow some things to pass through them but prevent other things from passing through.) to a region of low water concentration. This is seen in cell membranes. When there is a higher concentration of one type of molecule outside of a cell, water will move through a membrane out of the cell in order to make the water concentrations equal. This causes the cell to shrink (hypertonic). If the concentration of certain molecules is higher inside of the cell, then the water will move into the cell causing it to swell (hypotonic). When the molecule concentrations are equal on both sides of the membrane, water does not move (isotonic).
In the human body, many salts and enzymes help to regulate a cell’s state and...